A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphaltic shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphaltic strip material, either an organic felt or a glass fiber mat is passed through a coater containing liquid asphalt to form a tacky coated asphaltic strip. Subsequently, the hot asphaltic strip is passed beneath one or more granule applicators which apply the protective surface granules to portions of the asphaltic strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments on the hopper. In the manufacture of colored shingles, two types of granules are employed. Headlap granules are granules of relatively low cost for portions of the shingle which are to be covered up. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle which will be exposed on the roof.
To provide a color pattern of pleasing appearance the colored shingles are provided in different colors, usually in the form of a background color and a series of granule deposits of different colors or different shades of the background color. These highlighted series of deposits, referred to as blend drops, are typically made from a series of granule containers by means of feed rolls. The length and spacing of each mixture on the sheet is dependent on the speed of the feed roll, the relative speed of the sheet and the length of time during which the drop is made.
Not all of the granules applied to the hot, tacky, coated asphaltic strip adhere to the strip, and, typically, the strip material is turned around a slate drum to invert the strip and cause the non-adhered granules to drop off. These non-adhered granules, which are known as backfall granules, are usually collected in a backfall hopper. The backfall granules are discharged at a set rate from the backfall hopper onto the strip material.
One of the problems with typical granule application equipment is that the feeder rolls depend on mechanical movement (rotation) to index to the next position to enable another blend drop to fall onto the moving coated asphalt sheet. Usually the granules are discharged from a hopper onto a fluted roll from which, upon rotation, the granules are discharged onto the coated asphaltic sheet. The roll is ordinarily driven by a drive motor, the roll being positioned in the drive or non-drive position by means of a brake-clutch mechanism. This requirement for mechanical action has inherent limitations which prevent a very precise beginning and ending to the blend drop. Consequently, there is a limit to the sharpness of the blend drops on the shingle. As shingle manufacturing lines go up in speed the lack of sharpness is accentuated, and the distinction between the blend drop and the background color becomes fuzzy. The lack of sharpness puts a severe limitation on the kinds of designs and color contrasts which can be applied to the shingle.
Another cause of the impreciseness of typical granule depositing techniques is that the feeders depend on gravity exclusively, not only for directing the granules from the hopper to the moving coated asphalt sheet, but also for movement of the granules within the hopper itself. The use of gravity to move the granules within the hopper or discharge apparatus itself has granule feed rate limitations, and there is no easy way to control the rate of flow of the granules.
An improved means and method for depositing granules onto the moving coated asphalt sheet would eliminate the lack of preciseness inherent in the mechanical action of a fluted roll. Also, the ideal system would provide a means for enhancing gravitational forces in starting and stopping flow and would enable some means for controlling the flow rate of granules during deposition.